The present disclosure relates to sheet conveyance devices, document feeders, image forming apparatuses, and multi feed determination methods.
Image forming apparatuses including an image reading section to read an original document (sheet) may be provided with a sheet conveyance device to convey an original document to a reading point of the image reading section.
Such a sheet conveyance device includes a document conveyance path continuing from a document table to an exit tray via the reading point. A paper feed roller, a registration roller, and a plurality of conveyance rollers are provided in the document conveyance path in this order from the upstream side (the side of the document table) to the downstream side in the conveyance direction. Upon a start of original document conveyance, the paper feed roller supplies an original document loaded on the document table to the document conveyance path. The registration roller once stops transfer of the original document in the conveyance direction and conveys then the original document in the conveyance direction. The reading point is located downstream of the registration roller. The plurality of conveyance rollers convey the original document having passed over the reading point to the exit tray.
With this configuration, when the paper feed roller supplies an original document from the document table to the document conveyance path, a plurality of original documents may be supplied in an overlap fashion. For this reason, a separation roller to separate the overlapped plurality of original documents on a sheet-by-sheet basis is provided on the opposite side of the document conveyance path to the paper feed roller. In original document conveyance, the paper feed roller is rotated in the conveyance direction, while the separation roller is rotated in the reverse direction to the conveyance direction. Thus, even when a plurality of original documents are supplied in an overlap fashion, an original document not to be conveyed at the moment is returned to the document table.
For example, the separation roller is connected to a torque limiter. When paper feed power exceeds a critical value set in the torque limiter, the separation roller rotates in the forward direction (follows the movement of an original document sent in the conveyance direction to be rotated). While, when a plurality of original documents are supplied in an overlap fashion, an original document not to be conveyed at the moment is present between an original document to be conveyed and the separation roller. This restrains the paper feed power from exceeding the critical value set in the torque limiter. Thus, the separation roller rotating in the reverse rotation returns the original document not to be conveyed at the moment to the document table